Rechargeable battery systems for electric vehicles with purely electric drive and for hybrid vehicles and vehicles with fuel cell drive are the subject of current research. At present, preferably lithium-ion batteries are employed in the mentioned vehicle types, which are characterized by a high energy density and only a slight undesirable memory effect. The ability of a rechargeable battery to reliably supply electric consumers installed in motor vehicles with electric energy substantially depends on the thermal conditions prevailing in the surroundings of the battery. For the electrochemical processes which take place both during the provision and also during the absorption of electric energy—in the sense of recharging—which take place in the battery are dependent to a not unsubstantial degree on the operating temperature of the battery. Extensive research on different battery systems on lithium-ion basis have shown for example that below a critical temperature, for example in the region of approximately 0° C., the electric energy density made available by the battery greatly decreases compared with higher operating temperatures. Below this temperature, damaging of the Li-ion cell can additionally occur during charging.
Decisive for a reliable and trouble free operation of said batteries—this does not only apply to mentioned batteries on lithium-ion basis but generally also to any rechargeable battery systems—is also the creation of thermally well-defined ambient conditions. With a view to the substantial temperature fluctuations that occur during operation for example in a motor vehicle, this means that these have to be balanced through suitable temperature control devices which are thermally coupled to the battery in order to keep the ambient temperature of the battery—and thus also the temperature of the battery itself—constant within a predetermined temperature interval. Such a device has to be able on the one hand to increase the ambient temperature in the direct surroundings of the battery should the latter assume a value that is below the permissible temperature range. On the other hand, it must also be possible to lower the ambient temperature in the case that the latter exceeds this said temperature interval in upward direction.
From the prior art, various devices that can be thermally coupled to a battery are known, which as a rule comprise both a heating unit for increasing the battery temperature and also a cooling system for lowering the battery temperature.
Accordingly, a device for heating and cooling of a battery is described in DE 10 2009 90 588 19 A1, which comprises a coolant circuit and at least one electric heating element, both of which are arranged in a common heat transfer component. The electric heating element in this case is connected to the heat transfer component in a positively and/or non-positively joined manner. Characteristic for the device is that it requires a relatively large number of building elements, which during a heating operation are co-heated by the heating element due to the design, which significantly increases the heating output required for the actually aspired heating of the battery.